Starting from the center this time:
Tomodon is an amazing defensive core; Gastrodon, when invested in special bulk, takes on just about every special attacker that lacks a Grass-type move. Tomohawk itself is able to take on a fair number of special attacker Grass-types, but it really shines in patching up Gastrodon's vulnerability to physical moves.
But that's all of the obvious stuff. Let's take a look at why the rest of the team is there:
First of all, we need to look at the Pokemon that can give both Tomohawk and Gastrodon a bit of trouble. This category includes Tapu Lele, Tapu Koko with Grass Knot, Kerfluffle, Mega Crucibelle, Pajantom with Heal Block, Syclant with Tail Glow, Ferrothorn, Celesteela, Kyurem-Black, Lati@s(-Mega), Mega Mawile, Mega Medicham, and Mega Pinsir.
Hm, let's see if we can't patch up those weaknesses:
Pyroak easily resists STAB from Tapu Koko and shuts Ferrothorn and non-Air Slash Celesteela down entirely. Thanks to physical bulk investment, it is able to take Psyshocks from Choice Scarf Tapu Lele that could otherwise break past Gastrodon and shut down the rest of the team. Thanks to Gastrodon, Psychic on Scarf Lele is not too much of a concern, and thanks to Mega Crucibelle, neither is Choice Specs. Pyroak also handles the likes of Mega Mawile well, takes down Mega Medicham in conjuntion with Tomohawk and/or Scizor, and can even live a Return from Mega Pinsir. Stealth Rock also heavily discourages Kyurem-Black and Mega Pinsir from entering the field. Giga Drain is used instead of Leech Seed in order to help against some bulky Water-types this team might appreciate some help against; namely, Mega Swampert and Gastrodon. It also helps against Rotom-W and Keldeo.
Choice Band Scizor may not exactly be in vogue, but it certainly has its uses. It's always glad to pick off fast and weakened foes with an extremely powerful Bullet Punch. This is especially helpful against Syclant, Kerfluffle, and Mega Crucibelle, acting as speed control against them. It also does a hefty chunk to Kyurem-Black, OHKOing it if Stealth Rock is up. Pursuit is an extremely fun move on this set for eliminating the likes of Pajantom, Kitsunoh, Lati@s(-Mega), etc. especially against Psychic-types, where it sets up a 50-50 with U-Turn that can be mindgamed. U-Turn is there for predicted switches to physical walls like Tomohawk, Cyclohm, and Pyroak to prevent momentum killing by going into Kyurem-Black. Superpower nearly OHKOs Ferrothorn and 2HKOs Chansey, and for that reason I think it is very nice to have.
The goal on this one is simple: use Subzero Slammer to break through any of those annoying walls that are giving this team difficulty. Chansey? Gone. Pyroak? Gone. Celesteela? Gone. Ferrothorn? Gone. You name it and it's gone. And if it's not gone for Subzero Slammer, Earth Power and Fusion Bolt will catch it (Heatran, Arghonaut, Rotom-W, etc). We don't like stall in this household.
And finally, a wincon. After all those pesky physical walls I mentioned are gone and Scizor has taken out all those fast attackers, Mega Crucibelle has a fun time coming in, setting up with Coil, and cleaning up shop.